<?php
class Node {
	const NIL =  'nil';
	private $label;
	private $leftChild;
	private $rightChild;
	
	public function __construct($label = null) {
		$this->label = $label;
		$this->leftChild = null;
		$this->rightChild = null;
	}
	
	public function setLeftChild(Node $node) {
		$this->leftChild = $node;
	}
	
	public function getLeftChild() {
		
		return $this->leftChild;
	}
	
	public function setRightChild(Node $node) {
		$this->rightChild = $node;
	}
	
	public function getRightChild() {
		
		return $this->rightChild;
	}
	
	public function setLabel($label) {
		$this->label = $label;
	}
	
	public function getLabel() {
		
		return $this->label;
	}
}